Virginia Grape Disease Updates

Last night, we had several rain events which accounted for about 5 hours of wetness. Average temperature during that period was about 60F, and total amount of precipitation was 0.17 inches. It could be a light infection event for Phomopsis, powdery mildew ascospore discharge, and downy mildew infection. (little too short for black rot infection) I went back to the vineyard and took a look at the leaf lesions I showed here on Friday. Sure enough, there are sprangiophores (a tree-like structure containing spores) coming up from the underside of the leaf. As I mentioned in Friday's entry, it takes 1-2 weeks to develop spraongiophore, thus, the infection probably took place during 5/16-17 rains (I wrote 17-18th, but it was 16-17th). We are expecting few more chances of rains during this week. If your vines are close to bloom or blooming, please be ready to protect your vines.

Yesterday, thunderstorms passed by Frederick county from around 4 pm to 5pm. There were other rain events afterwards, and the relative humidity was high until 7:30 am or so. It accounted for >15 hours of wetness event with average temperature of 68F or so. Total amount of precipitation was 0.47 inches. It was warm and long enough for Phomopsis infection, powdery mildew ascospore discharge, black rot infection, and downy mildew infection. Also, now we are having 5 consecutive nights with temperature above 55F with the relative humidity in 80-100% range which can promote downy mildew sporulation. Speaking of downy mildew, I started to see potential downy mildew lesions on some of our untreated vines. Typically, after infection, "oily spot" will show up on the upper surface of a leaf, then you will see "downy" fungal body on the underside of the leaf. This downy fungal body mainly consists of many sporangiophores which look like a tree of sporangium. Spo...

In the past few days, we had about 2 inches of rain at Winchester, but I heard that there were up to 5 inches rains observed in some places. Since the afternoon of May 25th, we have been having either rain or high relative humidity conditions continuously (RH is still above 90% as of 10:30pm 5/28/09, thus potentially, we have > 60h of wetness). Average temperature during this period was 67F in 25th, and 60F in 26th and 27th. These conditions are good enough for Phomopsis infection, powdery mildew ascospore discharge, black rot infection, and downy mildew spore production and infection. If your vines are very close to bloom or blooming, it is the critical timing for many of these disease development. As I mentioned earlier, there are some fungicides you can use after infection events. For powdery mildew, you can use any of fungicides you typically use (even sulfur) because the fungus grow on grape tissue superficially. For black rot, Rally (mycrobutanil) has a good curative ...

It looks like we will have a rainy week. Since Saturday, we had three nights with average temperature above 65F with the relative humidity in 80% or more at Winchester. These warm humid nights are favored by downy mildew sporulation from infected leaves. And these series rain events will help them to infect leaves, rachis, and berries. Thus, it is possible that downy mildew had a chance to produce spores during these nights, and these spores are ready for infecting grape tissues. Therefore, for the next round of application, you may want to think about adding a fungicide for downy mildew with curative activity such as Ridomil products. But once again, the risk of diseaes development depends on the history of your vineyard and other environmental conditions such as variety, traning system, etc. If downy mildew has not been a problem in the past, the risk may be less.

There was a sprinkle in the morning, but so far, we haven't experienced a significant rain event yet at Winchester. Our Chardonnay and Cabernet sauvignon have been moving its growth stage. It was about 8-90% with 8-9 leaves unfolded with elongation of rachis (E-L 15) for Chardonnay, and about 3-50% E-L 15 for Cabernet sauvignon. Cab sauvignon has more variation among vines, which is consistent since bud break. I start to see development of black rot lesions on untreated vines. It takes 2-3 weeks to develop fruiting bodies (black specks within tan colored lesion), thus, rain events during 5/5-5/7 or 5/11 are probably responsible for the infection. I hope you do not see many of these symptoms in your vineyard. If so, you need to protect your berries very well so that it won't affect your yield. Mancozeb, captan, and azoxystrobin (Abound) works well as a protective fungicide application, mycrobutanyl (Rally) works well as a curative fungicide, but I doubt that it will kil...

(Today's picture is our friend Phomopsis again! Left side has more spots probably because it is closer to the vine where the fungus survives and produce spores. Spores were rain splashed to the leaf to cause infection.) It seems that pretty much all over Virginia is expecting some type of rain during next few days. I do not know how "30-40% chance of thunderstorm" turns out, but if your last spray was more than two weeks ago and/or your vines have grown a lot from the last application, then you may need to be prepared for these chances of rains. As I noted yesterday, please adjust your spray materials and spray amount based on your vine's growth stage.

I appreciate those of you who showed up at the meeting. I'll try to visit the meeting in the other regions as much as possible. [I do have a research to do, so, I cannot go to every single one of them, though. ;)] It looks like we will have good weather during next few days, and I think most of you are thinking about pre-bloom or at-bloom applications right now. (Those of you in the Southern VA may be thinking about 1st application after bloom.) Temperature is getting higher (although we had 3-4 days of cool nights), and many of common disease organisms are more active around 60-75F. At pre-bloom, you need to think about Phomopsis, powdery mildew, black rot, and downy mildew control, and for at-bloom or the first application after bloom, you need to add something for Botrytis control. Pre-bloom to 2-3 sprays post-bloom are very critical sprays for disease control in VA growing area. Rachis and flower part can be infected by these fungi and results in direct problems, and ...

A vineyard meeting will be held at Nelson extension center (just south of Food Lion on Thomas nelson Highway (Hwy 29)) at Lovingston from 11 am. I'll be talking about the same early season disease management information I presented at the previous meeting . The temperature in the morning did not go down enough to cause damage on our vines. I hope your vines are OK as well. These two nights are too cold for disease development. Our Chardonnay was ~90% 7~8 leaves unfolded (I have not observed rachis elongation yet), and Cabernet sauvignon was about 8-90 % 7~8 leaves unfolded. I'll probably apply pre-bloom applications in the near future.

Our low was low 40's this morning. It suppose to be warmer tomorrow and I hope that we do not get any frost damage. We'll see. We received several disease samples today which I'd like to share with you. The first one is crown gall. This is caused by a bacterium called Agrobacterium vitis . This gall formation is due to genetic modification caused by the bacterium to the infected grape vine. Sometimes it is only a cosmetic damage, but the gall tissue could girdle the vine and restrict the movements of water and nutrients, then results in the death of the vine. There are some chemicals and biological agent available against gall formation and prevention of the disease, but as far as I know, none of them are very effective as you would expect from other chemical treatments such as fungicides. Removal of the infected vine and then replacing with a certified vine is the common method of management. However, you need to keep in your mind that this bacterium can survive i...

As you may noticed, temperature has been declining since this morning. National weather service is issuing frost advisory from 4 to 9 am tomorrow (Monday) morning for Frederick county. Please check your local weather. Recent series of rain events are providing enough moisture to vines to push their shoots rapidly, and these succulent tissues are sensitive to stresses. If you are the lucky one with one of air circulation systems (propeller etc), this may be the time to use it. Hopefully, your vines won't experience frost damages. Our Chardonnay was about 80% 7-8 leaves unfolded (~10-inch or longer), and Cabernet sauvignon was about 20% 7-8 leaves unfolded (7~10-inch) as of today. (Phomopsis symptoms on a vine in our experimental vineyard, 5/17/09) As for disease concerns, we experienced rains and thunderstorms yesterday from 6:20 pm to 10 pm, then there are light rains here and there until 2 am or so. The relative humidity was above 90% until 3:20 am. Temperature started of...

It turned out to be a very nice day for planting at Winchester. We almost finished planting of two vineyards (a total of 1/2 Acre with Chardonnay and Merlot) which will be used for chemical trials and other management-related experiments. We had a drizzle in the early morning, but the expected thunderstorm did not arrive until 8pm or so and it was not as severe as I expected. On 14th, night time relative humidity was high, but temperature was low (low 40's), thus it was not a disease night. But last night, we had a series of short rains and temperature stayed in low-60's with the relative humidity above 90% until now (8am, fog). This >12 hours of wetness accounts for Phomopsis, black rot, powdery mildew, and downy mildew infection events. We are expecting to see more rains during this weekend, so, please think about potential disease events (in the future or in the past) when you decide for a fungicide application. You can find details of infection events I'm d...

Thank you for those of you showed up at the vineyard meeting, and we thank Jeff to host the meeting. The notes I used at the meeting can be downloaded from here . Last night was another cool night around Winchester. The relative humidity was high (~90%), but average temperature was 48F or so, and it was little too cold for downy mildew sporulation. We are expecting some thunderstorms passing by during next few weeks, and temperature is expected to be in 70's. Depends on when your last application was made and how much new growth you have observed, you may need to protect new growth against this series of rains. I'll be planting my vines tomorrow. I hope I won't be rained out...

We are having nice sunny days! Some of shoots in our Chardonnay elongated to 10-inch or so (start to passing E-L 12 stage). And Cabernet sauvignon is catching up with Chardonnay. About 7-80% of shoots are 5~7-inches (E-L 12). A day before (5/11/09), we had fairly dry (~50% RH) night. We had a shower (0.03 in) in the yesterday evening (5/12/09). It lasted only 40 min or so and the RH did not stay high, thus it probably was not enough for any disease event. The night time RH was high (nearly 100%), but temperature was in mid-40s. Thus, it was not good for downy mildew spore production either. We will have a vineyard meeting at Glenn Manor vineyard and winery from 11 am tomorrow. I'll talk about early season disease management tips as I did last time, and this time it includes information on downy mildew. If you cannot make it, you can download my notes from here .

It has been a very sunny weekend in 70's. I can take this anytime. Last night, RH was 4-50% and temperature was around 64F. I think it was little too dry for downy mildew to be happy. Speaking of disease, I found some leaves and canes showing an initial symptom development of Phomopsis today. We have untreated vines for disease observations, and I'm hoping that these vines will provide us nice cases of diseases throughout the season. The hard-to-see dark spots with yellow hallo are from Phomopsis infection on leaf. If you take a look at shoots, what you see is: Small necrotic spots (around the center) which can be expand later in the season. Dr. Mike Ellis' group at the Ohio State is currently working on the infection process of this fungus. Based on observations on the production of the fruiting structure in my previous experiments, it looks like this fungus can spread underneath the epidermal tissue even if we do not see clear symptoms. At which point the sp...

At Winchester, we did not experience the forecasted rain event yesterday (5/08/09). It was a light shower in this morning with trace amount of precipitation. One thing I noticed was the night time temperature. It was above 68F with relatively high relative humidity (mostly in 8-90% range). Under this condition, downy mildew fungus (it's not technically a fungus, but I call it fungus for convenience) can produce a structure called sporangiophore which is basically a tree of sporangia which contains spores called zoospores. Typically, we consider the risk of spore production is high when there are more than 3 consecutive nights with temperature above 55F with high RH. Night time temperature in last few days are (5/6/09: lower 50's, 5/7/09: lower 60's, 5/8/09: lower 50's, and 5/9/09: upper 60's), and you know the RH was high. The first potential infection event was on 5/4/09 around Winchester, and it takes 7 days (depends on temperature) to produce spores. Eve...

As you probably noticed, the sun is out! And grape vines are moving fast. Our Chardonnay and Cabernet sauvignon has moved quite a bit as well. About 7-90% are 5-7 inches (E-L 12) and about 5-70% are 5 inches (E-L 12) for Chardonnay and Cab sauvignon, respectively. Yesterday (5/07/09), Winchester area had a brief shower (0.12 inches) from 10:25am (64.4F) to 12:00pm (64.4F), and the RH was >90% until 1:00pm. And then a very short thunderstorm from 3:40 to 4:00pm (69.8F). The first event was bit short for Phomopsis and black rot infection events; however, it was probably enough for powdery mildew ascospore discharge and downy mildew infection event. A mild temperature range favors both mildew pathogens too. Some of varieties are probably getting closer to the bloom, and you need to start thinking about these mildews. 2-3 weeks pre-bloom is the start of critical period for downy mildew rachis and berry infection. Make sure that your spray program has something against downy...

At Winchester, yesterday's (5/6/09) rain started from 5pm (60.8F) and ended at 6:40pm (59.0F); however, the RH was >90% until this morning (8:40am). A total amount of precipitation was 0.05 in. Thus, it probably accounted for >14h of wetness with upper 50's in temperature (F). It would be enough for Phomopsis, powdery mildew ascospore discharge, black rot, and downy mildew infection. (I feel like I'm repeating myself...) Please do not get overwhelmed by my report of infection events. I'm just giving you the information about what could happen based on weather conditions observed. If you applied your protective fungicide application, it should stop infection. In addition, there are chemicals with curative (or kick-back) activity against powdery mildew, downy mildew, and black rot. Moreover, the risk of infection by these fungi depends on the history of your vineyard too. For example, if you had a history of outbreak of downy mildew year after year, you t...

Plenty of water affected growth too. About 10% of Chardonnay were 5-7 inches (E-L 12). Growth of Cabernet sauvignon was not as dramatic as that of Chardonnay. As with yesterday, 6-70% of shoots are 3-inch (E-L 9) and others are 1-2 inches.

Yesterday's (5/5/09) precipitation at Winchester was 0.27 inches starting from 4:20pm (55.4F) and ended at 9:20pm (53.6F); however, the relative humidity was almost 100% until midnight. Thus, >8 hr of wetness with mid 50's temperature probably accounted for Phomopsis light infection, powdery mildew ascospore discharge, and downy mildew infection. We had overcast weather this morning, and I hope that you had a chance for application (if needed). We are expecting more rain in next few days and next break could be during this weekend.

We experienced a whole day of rain yesterday (5/4/09). Average temperature was 52F, and amount of precipitation was 0.76 inches. The total length of rain event was over 30 hours, including a day before and early this morning. Needless to say, it was long enough for Phomopsis, powdery mildew, and black rot. Our Chardonnay had grown since the last observation. Average was about 60% 3-5 inch stage. Cabernet sauvignon still varies with vines, some vines are showing 6-70% 2-3 inch stage and others are showing 7-80% 1-2 inch stage. We are having a break from rain today in most of central and northern VA. I hope those of whom with concern on Phomopsis had a chance to apply your treatment.

The ongoing rain event since yesterday morning (5/3/09, 8 am) has been relatively cold. Starting temperature was about 52F, at mid-night it was 49F, and it has been lower 50's today. It is low, but long enough (>33 hr so far) for Phomopsis to cause light (5-15% disease severity on a cane) to moderate (15-25%) disease. In addition, as of this morning, we have received 0.84 inches of rain since last week (and it’s still raining as of 4 pm, but looks like the end is coming!!). As for powdery mildew ascospore discharge, this rain event met the requirement. A typical rule of thumb for fungicide re-application is “2 weeks or 1 inch of rain, whichever comes first” (Note: you need to adjust the time between applications based on the growth of vine). Please check your local weather for rain and temperature information. There is a banner of “weather underground” on the upper-right side where you can check your local weather information in detail by typing in your zip code (you can even...

Update on growth stage: Chardonnay was about 70-90% 3-inch growth; Cabernet sauvignon was still about 50% 1-2 inch growth with a variation among vines. Still raining as of 6:45pm...

Yesterday, Winchester had a drizzle during 3-4am with an average temperature of 58F. It was not a major rain event; however, the relative humidity was almost 100% until 10am. In addition, we had a rain event from 8:30 to 9:30am with an average temperature of 55F. A combined precipitation was 0.08 inches. If you separate these events, it was not enough for Phomopsis to cause disease. However, since the relative humidity was high during the night, I tend to think it was a continuous event. If we combine both rain events, it was enough for a moderate infection (15-25% severity) for Phomopsis. Considering how wet it has been, ascospore discharge of powdery mildew was probably initiated with these rains (especially after 3 am one) whether you combine events or not. (but the morning rain might have washed spores off from leaves... a wishful thining ;)) I was running 10K for Apple blossom festival during the morning rain. It brought temperature down and was nice for me, and after...

At Winchester, we had rain from 11:50am to 2:20pm (0.12 in) with starting and ending temperature of 62.3 and 67.8F, respectively. Relative humidity dropped soon after the rain and still declining at 5pm and the wind was constantly blowing at 5-10 mph, thus, leaves are probably dried one hour or so after the rain. (If the leafwetness measurement is not available, I use RH>90% as an indicator for the leafwetness after the rain.) Three hours or so was not enough for Phomopsis infection, but it was warm enough for powdery mildew ascospore discharge. Yesterday (4/30/09), we took an advantage of a calm cloudy day and applied our first fungicide application (mancozeb 3 lb/A + sulfur 3 lb/A). Primary target at this point is Phomopsis and Powdery mildew. Although it was either raining or overcast, average temperature in the past few days were in 50's and 60's, and grape were moving its growth stage. About 70% of our Chardonnay was 3-inch stage, and Cabernet sauvignon was abo...